OBJECTIVES: For the overall project the objective is to determine the stereochemical courses of enzymatic bond cleavage reactions at phosphorus, with special reference to whether inversion or retention of stereochemical configurations occurs at phosphorus in substrates for nucleotidyltransferases and phosphotransferases. For the current year the principal objective has been to devise methods for preparing sulfur analogs of ADP and ATP having chiral 0-16, 9-18, S substituted terminal phosphorothioate groups.